Water intake systems use various types of screens and barriers when obtaining water from a lake, a river, or other body of water. As will be appreciated, submerged screen intakes can attract debris as floating material becomes attached to or rests on the screen's surface during operation. Eventually, this material can block the screen and reduce its flow capacity.
Several systems have been developed to clean debris from screen intakes. For example, mechanical systems that use moving brushes have been used to clear screens of debris. In addition, removable forms of screens have been used in many locations to overcome cleaning issues.
In other implementations, airburst cleaning systems can use bursts of air directed from a header to clean the screen of debris. The air cleaning system can be used on single screens or on multiple screens through a manifold of valves. In the airburst cleaning system, a compressor fills a receiver tank to store a volume of compressed air at an appropriate pressure. In a cleaning cycle, a rapid open/close valve releases the air from the receiver tank, and the released air passes through connective piping to deliver the airburst to a submerged screen intake. Within the intake, the airburst displaces several times the volume (normally 3 times the volume) of the screen.
As one particular example, Johnson Screen's Hydroburst System is an air backwash system used for cleaning cylindrical screen intakes with an airburst. FIGS. 1A-1C show a water intake system 10 having an air backwash system 20 according to the prior art for implementations where the screen intake 30 may need regular cleaning when exposed to debris or when the screen 30 is difficult to access. When operated, the air backwash system 20 flushes the debris away from the screen's surface by releasing a large volume of compressed air in a quick burst inside the screen 30.
As shown in FIGS. 1A-1B, the air backwash system 20 has a receiver tank 22 that stores compressed air and has a compressor 24 that charges the tank 22 with the compressed air. Distribution piping 28, valves 25, and the like couple the tank 22 to a header in the screen 30, and a control panel 26 controls operation of the system 20.
The cylindrical screen intake 30 shown in FIG. 1C has a tee configuration with two screens 36 on opposing ends of a central body 34. A water outlet 32 connects from the central body 34 and connects to other components of the water intake system 10. Air backwash headers 40 disposed in the screens 36 connect to an inlet pipe 42 that receives air from the air backwash system 20. When an airburst communicated from the air backwash system 20 reaches the headers 40, the resulting burst of air/water can clean the cylindrical screens 36 of debris.
Cleaning a screen with an airburst can also be used for flat screens, which can be used for a number of applications, including water intake systems and fish diversions in dam and rivers to protect fish from hydroelectric turbines and pumps. Typically, the flat screens for these applications have a low-suction velocity to protect fish and other aquatic life. Yet, debris may still collect on the flat screens.
One solution by Montgomery Watson Engineering for clearing debris from a flat screen is shown in FIGS. 2A-2B. A water intake module 50 buries in a bed of a waterway so that a portion of the module 50 sticks above the bed. The module 50 has a nose shield 54 at its upstream end. A supply pipe 56 runs from the module 50 to a water intake system, and a cleaning air pipe 60 and a buoyancy air pipe 65 run from the module 50 to components of an air supply system.
Internally, the module 50 contains flat screens 52, flow control slats 64, airburst cleaning pipes 62, floatation tanks 67, and a supply pipe connection 55. The flat screens 52, slats 64, and airburst pipes 62 situate at the top of the module 50, while the floatation tanks 67 situate at the bottom. The cleaning air pipe 60 of FIG. 2A connects to the airburst pipes 62 shown in FIG. 2B, and the buoyancy air pipe 65 of FIG. 2A connects to the flotation tanks 67 shown in FIG. 2B.
During use, water flows downward through the flat screens 52 and past the slats 64 into the module's collection chamber where the water can then travel to the supply pipe 56. The airburst pipes 62 are horizontally arranged PVC pipes located between the flat screens 52 and slats 64. These pipes 62 have small holes and distribute an airburst for cleaning the flat screens 52 when a burst of air is supplied. The slats 64 and pipes 62 have been used with horizontal modules 50 as shown in FIG. 2B, but they have also been used for vertical modules (not shown).
Another solution from Johnson Screens for clearing debris from a flat screen is shown in FIGS. 3A-3C. Here, a horizontal manifold 70 is used to clean a flat screen 52. The manifold 70 has distributor pipes 72 enclosed by troughs 74. A manifold frame 76 couples to the screen 52 or anchors by suitable stabilizing means downstream of the screen 52. Either way, the manifold frame 76 supports the deep troughs 74, which facilitate airflow from a backwash system 20 to the screen 52. As best shown in FIG. 3C, the troughs 74 have back panels 75, which can be solid as shown. Alternatively, the back panels 75 can be perforated or may not be present so water can flow through the deep troughs 74.
To provide the airflow, a conduit 73 couples from the backwash system 20 to each distributor pipe 72 enclosed in the troughs 74. Each distributor pipe 72 has a plurality of orifices (not shown) to direct a burst of air outwards toward the screen 52. When the backwash system 20 produces an airburst, for example, the air is directed from the pipes 72 and troughs 74 to the opposing screen 52 to clear debris. Water flow through the screen 52 and between the troughs 74 is shown by arrows.
Although using compressed air in the airburst systems to clean screen intakes is effective, the airburst systems release a great deal of air in a short period of time in proximity to the submerged screen intake. Depending on the body of water in which the screen is situated, there may be concerns about how the release of the airburst can cause disturbances that affect boaters or other users of the waterway or that affect nearby wildlife or fauna where the submerged screen is installed.
Blockage of screen intakes by frazil ice is another concern when the screen intakes are situated in certain bodies of waters. During winter, super cooled water (below 32F) can form small needles or pieces of frazil ice under certain weather conditions. The frazil ice can eventually coat and block a submerged screen intake. As expected, removing the frazil ice from the submerged screen can be particularly difficult.
Some techniques have been used to prevent blockage of a submerged screen intake or trash rack from frazil ice. For example, a diffused flow of heated water can be introduced into the intake system upstream of a trash rack. Alternatively, the metal trash racks or screens can be electrically heated. In another solution to minimize the buildup of frazil ice, bars composed of HDPE have been used for coarse screens, and polyethylene panels have been used for fine screens. Additionally, a warm water injection system has been used to recirculate discharge water to electric heaters and to then mix the heated discharge at the intake with the water delivered from the river. When this is done, the heated water combats the buildup of frazil ice on the intake.
Although these solutions may be effective to deal with frazil ice, they can be difficult to implement and maintain, or it may not be possible to use them in some implementations.